1. Field of the Invention
The present invention relates to a novel process for preparing 3,4-dihydro 2-naphthanoic acids or esters thereof by heating an alpha-vinyl cinnamic acid or ester thereof to attain cyclization. The invention also relates to a process for preparing 2-naphthanoic acids or esters thereof by first obtaining a 3,4-dihydro 2-naphthanoic acid or an ester thereof as indicated above, and then dehydrogenating this compound to obtain the corresponding 2-naphthanoic acid or ester thereof.
2. Description of the Background
Substituted 2-naphthanoic acids and esters thereof are useful as polymer intermediates in the chemical industry. However, the methodology for making these compounds is very sparse. The major problem posed by the synthesis of these compounds is that for the 2-naphthanoic acid derivatives to be useful as polymer intermediates, a second functional group besides the carboxyl group must be present. Moreover, such functional group must be present at a specific location on the molecule. Thus, a single, specific isomer of a disubstituted 2-naphthanoic acid or ester thereof must be produced out of a potential 14 distinguishable isomeric naphthanoic acids. The development of such a process is of great significance to the industry. Dihydronaphthanoic acids or esters particularly the 3,4-isomer, are particularly valueable substituted 2-naphthanoic acids.
A number of methods have been known to produce dihydronaphthalenes, including one with a pyrolytic approach similar to the present invention (Volkovitch, P. B., Conger, J. L., Castiello, F. A., Brodie, T. D. and Webber, W. P., J. Amer. Chem. Soc. 97: 901 (1975); Radcliffe, M. M., and Webber, W. P., J. Org. Chem. 42: 297 (1977); Rosen, B. I., and Webber, W. P., Tet. Lett. 51 (1977); Rosen, B. I., and Webber, W. P., J. Org. Chem. 42: 47 (1977)). However, none of the prior art methods are applicable to the synthesis of 3,4-dihydro 2-naphthanoic acid derivatives with a predictable substitution pattern.
Specific 3,4-dihydro-2-naphthanoic acids have been synthesized by the prior art (Myrboh, B., Ila, H., Junjappa, H., J. Org. Chem. 48: 5327 (1983); Dinulescu, I. G., Georgescu, E. G., Stanescu, L., and Avram, M., Tet. Suppl. 1, 37: 55 (1981); Vebrel, J., and Carrie, R., Bull. Chim. Soc. Fr., Part II: 116 (1982); Ito, Y., Yonezawa, K., and Saegusa, T., J. Org. Chem. 39: 2769 (1974)). However, none of these specifically tailored methods are applicable to the general class of naphthanoic acid derivatives synthesized by the process of this invention.
Accordingly, there is still a need for a general process for the synthesis of dihydronaphthanoic acid and naphthanoic acid derivatives having a predictable substitution pattern.